1. Field of the Invention
The present invention relates to a wire-stacked transformer, and more particularly, to a wire-stacked transformer capable of improving the efficiency of a power amplifier with its loss reduced.
2. Description of the Related Art
In general, wireless communication equipment such as hand-held terminals employs semiconductor chip devices serving as radio-frequency communication circuits. It is very important to build a single chip including a transmitter and a high-frequency power amplifier having a suitable power level with respect to a material cost reduction and efficiency of the transmitter. To build such a single chip, both the power amplifier and transmitter are built as complementary metal-oxide-semiconductor (CMOS) devices. However, CMOS devices have difficulties implementing a power amplifier due to their low breakdown voltage and substrate resistance. As such, technologies for building the power amplifier which overcome such low breakdown voltage and substrate resistance are highly desirable for improvements of output power and efficiency of the integrated-circuit amplifier.
The distributed active transformer (DAT) is used to boost the breakdown voltage of such a power amplifier.
FIG. 1 is a circuit diagram for showing a conventional DAT. As shown in FIG. 1, the DAT has a first loop 10 supplied with electric power, a second loop 20 generating induction current by current flowing in the first loop 10, and plural power supply units 60 for supplying electric power to the first loops 10.
The first loop 10 is formed with four metal plates disposed to form a rectangular shape, and each metal plate serves as a drain tuning inductor resonating with parasitic transistor capacitance and for controlling a harmonic signal. In here, the metal plate inductor has a Quality factor (Q-factor) higher than a spiral inductor.
The power supply units 60 are disposed between neighboring metal plates and thus interconnect cathode terminals of the output ports of the respective metal plates. Each power supply unit 60 is formed with a pair of transistors, the sources of which are interconnected and commonly grounded. The gate of one of the transistors is driven with a positive phase signal, and the gate of the other transistor is driven with a negative phase signal. Such power supply units 60 cause substantial AC ground to be formed at each corner of the first loop 10.
The second loop 20 is formed with a metal plate of a rectangular frame shape forming one loop, and each side of the metal plate serves as one metal coil. That is, the second loop 20 generates induction current caused by the first loop 10 and serves as the second loop of the transformer.
The loss of such a DAT affects the efficiency of the whole power amplifier module, and, in particular, the DAT has a drawback of degrading the efficiency of the whole power amplifier due to its inherent large power loss when it is used as an output matching circuit of the power amplifier.
In general, as the metal plates forming the first loop 10 and the second loop 20 become thicker, the distance between the virtual centers of the first loop 10 and the second loop 20 becomes shorter. It is to be noted that the virtual center refers to a substantial centerline of a magnetic field forming when electric current flows in the first loop 10 and the second loop 20. Since the first loop 10 and the second loop 20 in the conventional DAT form a single loop respectively, the centerlines of the first loop 10 and the second loop 20 become a line connecting the center of the metal plate in the transverse direction of the metal plate forming each loop, respectively.
However, the thickness of the metal plate forming each loop of the DAT is generally determined at the time of the production process, and since the first loop 10 and the second loop 20 are formed in a single loop in the current DAT structure, respectively, the virtual centers of the respective loops are inevitably and considerably spaced apart from each other.
Accordingly, a method which can compensate for the above shortcomings, which do not have the metal plate of the DAT itself become thicker, thereby improving the efficiency of the power amplifier with reduction of DAT loss.